Regional military spokesman Lt. Col. Randolph Cabangbang said the fighting erupted at dawn Tuesday near Al-Barka town on Basilan island when troops were investigating reports of rebel incursions. Sporadic clashes continued late into the night in the remote region, he said.

At least 13 soldiers were killed and 11 wounded, and 10 others were missing, he said.

Moro Islamic Liberation Front spokesman Von Al Haq said at least three rebels were initially killed in the clash, but police reported at least six rebels were killed.

Al Haq said government troops provoked the fighting by attacking the rebels in their Al-Barka stronghold in violation of an existing cease-fire. Army troops shelled the rebel stronghold after the initial clash, trapping villagers in the fighting, he said.

"The Philippine army is continuously bombarding the area where innocent civilians are being caught in the middle of the ferocious artillery strike," the rebels said in a statement on their website. "This attack of the government forces blatantly violated the existing ceasefire accord."

Cabangbang said troops were deployed to check reports by villagers that a group of gunmen known to be holding kidnap victims had strayed in areas close to their communities. He said the troops did not intrude on the guerrilla stronghold, and were about two miles (4 kilometers) from it when they were fired upon by the Moro rebels, prompting the troops to fight back, he said.

Cabangbang said the military believes the gunmen included a former rebel commander identified as Dan Laksaw Asnawi, who escaped from a Basilan jail in 2009 with 30 other inmates. Asnawi was detained for his alleged involvement in the beheading of 14 marines during a 2007 clash in Al-Barka, Cabangbang said.

"When we're running after a criminal and get near their area, they cannot just kill our soldiers," Cabangbang told The Associated Press by telephone.

The Moro rebels who clashed with troops were with al-Qaida-linked Abu Sayyaf militants, he said. Al Haq countered that rebels from his group do not operate with the violent Abu Sayyaf.

Cabangbang said special army forces were searching for the missing soldiers in Basilan, a predominantly Muslim island about 550 miles (880 kilometers) south of Manila.

Al Haq said an army general called him seeking the safe release of the missing soldiers if they were in rebel custody. Al Haq said he replied that his group could not immediately reach their fighters by phone to ask if they were holding military captives.

The 11,000-strong rebel group has waged a bloody insurgency for self-rule in the southern Mindanao region, the homeland of minority Muslims in the predominantly Roman Catholic country. The conflict has killed more than 120,000 people and stunted development of the resource-rich but impoverished south.

Malaysian-brokered peace talks between the rebels and the government received a major boost in August when President Benigno Aquino III met rebel chairman Al Haj Murad Ibrahim in Tokyo to bolster the negotiations.

The rebels, however, rejected a government proposal for Muslim autonomy when talks resumed a few weeks later in Malaysia but they said they will continue with the talks.